1. Technical Field
The invention relates to a power conversion technique. Particularly, the invention relates to an inverter and a direct current bus voltage regulating method thereof.
2. Related Art
In design of a general inverter, a basic condition for implementing a normal operation of the inverter is that an amplitude of a direct current (DC) bus voltage is not smaller than a peak of an alternating current (AC) output voltage. In other words, regarding the inverter adopting a multistage conversion circuit configuration, especially a two-stage inverter composed of a DC-DC conversion circuit and an inverting circuit, in order to ensure a normal operation of the inverter, a power conversion operation performed by the DC-DC conversion circuit of the previous stage has to be sufficient to make the output DC bus voltage to be complied with the aforementioned condition.
To achieve a basic requirement of the above design, a designer generally designs the inverter by stably controlling the DC bus voltage to a constant voltage value. However, since a magnitude of the DC bus voltage is actually varied along with variation of a DC input voltage received by the DC-DC conversion circuit, in some applications (for example, a photovoltaic grid-connected system), it is not easy to maintain the DC bus voltage stable.
Moreover, if only the DC bus voltage is designed to the constant voltage value, the inverter may have low conversion efficiency when the constant voltage value is far greater than the DC bus voltage required by the post-stage inverting circuit.